Mist generating apparatus

ABSTRACT

An improved mist generating apparatus is provided, the apparatus having a longitudinal axis (L), and first and second opposing nozzle surfaces ( 100,102 ) which define a nozzle between them. A first process fluid passage ( 28 ) has an inlet connectable to a supply of process fluid, and a process fluid outlet ( 110 ) on one or the first and second nozzle surfaces ( 100,102 ) such that the process fluid owlet ( 110 ) opens into the nozzle. The nozzle has a nozzle inlet ( 104 ) connectable to a supply of driving fluid, a nozzle outlet ( 108 ), and a throat portion ( 106 ) intermediate the nozzle inlet ( 104 ) and nozzle outlet ( 108 ). The nozzle throat ( 106 ) has a cross sectional area which is less than that of both the nozzle inlet ( 104 ) and the nozzle outlet ( 108 ). The nozzle extends radially away from the longitudinal axis (L) such that the nozzle defines a rotational angle about the longitudinal axis (L). A centre line (CL) of the nozzle extends from the nozzle throat ( 106 ) to the nozzle outlet ( 108 ) at an angle of between 50 and 80 degrees relative to the longitudinal axis (L).

The present invention relates to the field of mist generation, and moreparticularly to an improved twin-fluid mist generating apparatus capableof spraying mists over a spray angle of 360 degrees about the apparatus.The present invention is particularly suited to applications in thefields of fire suppression, decontamination, disinfection, dustsuppression, particle tie-down and cooling.

Twin-fluid mist generating apparatus generate a spray mist by theinteraction of a first driving fluid with a second process fluid. Suchapparatus which can spray mists over a spray angle of substantially 360degrees are known. These apparatus utilise a nozzle which extends aroundthe entire circumference of the apparatus and which is at substantially90 degrees to the longitudinal axis of the apparatus. As a result, innormal operation (where the apparatus is mounted on a horizontal surfacesuch as a floor or ceiling) the apparatus will spray a mist over a 360spray angle, with the mist exiting the nozzle substantially parallel tothe surface upon which the apparatus is mounted.

In certain applications the location of the mist generating apparatus ina room or enclosed space is dictated by operating requirements of thatroom or space. For example, in decontamination applications targetinginsects, spores or fungi in warehouses storing perishable goods it isusually necessary to place the mist generating apparatus as close to theceiling of the room as possible, or locate the apparatus in a ceilingrecess, so that the apparatus does not interfere with the movement ofgoods, vehicles or cranes within the room. Similarly, in decontaminationand fire suppression applications in hospitals and other publicbuildings the apparatus is preferably placed as close to the ceiling ofa room as possible, so that it cannot easily be interfered with oritself interfere with the movement of people and equipment within theroom. Additionally, in fire suppression or protection of enclosed spacesit is usually necessary to place the mist generating apparatus as closeto the ceiling of the space as possible, or else locate the apparatus ina recess in the ceiling, so that the apparatus does not interfere withthe movement of goods, vehicles or equipment within the space.Positioning the mist generating apparatus in this way can limit theperformance of the apparatus, as if the apparatus is too close to themounting surface spray droplets issuing substantially parallel to thesurface are likely to be attracted towards, and possibly land upon, themounting surface rather than continuing into the volume being filledwith mist. The droplets then coalesce on the surface, creating largerdroplets which eventually drop off the surface rather than reaching theextremities of the volume. The problems can be even more pronounced whenthe apparatus is recessed, with the majority of the spray dropletssimply coalescing on the surfaces of the recess rather than travellingout into the space. Thus, the ability of the mist generating apparatusto spray a mist into the furthest reaches of an enclosed space can berestricted when the apparatus is mounted close to a surface or within arecess.

It is an aim of the present invention to obviate or mitigate thesedisadvantages of this type of mist generating apparatus.

According to a first aspect of the present invention, there is provideda mist generating apparatus having a longitudinal axis and comprising:

-   -   first and second opposing nozzle surfaces which define a nozzle        therebetween; and    -   a first process fluid passage having an inlet connectable to a        supply of process fluid, and a process fluid outlet on one of        the first and second nozzle surfaces such that the process fluid        outlet opens into the nozzle;    -   wherein the nozzle has a nozzle inlet connectable to a supply of        driving fluid, a nozzle outlet, and a throat portion        intermediate the nozzle inlet and nozzle outlet,    -   wherein the nozzle throat has a cross sectional area which is        less than that of both the nozzle inlet and the nozzle outlet;    -   wherein the nozzle extends radially away from the longitudinal        axis such that the nozzle defines a rotational angle about the        longitudinal axis; and    -   wherein a centre line of the nozzle extending from the nozzle        throat to the nozzle outlet is at an angle of between 50 and 80        degrees relative to the longitudinal axis.

The centre line of the nozzle is a line which divides the nozzle intoequal upper and lower parts when the nozzle is viewed in cross section.The centre line extends through points at the nozzle throat and nozzleoutlet which are equidistant the surfaces defining the nozzle throat andnozzle outlet, respectively.

References to “radial” and “radially” in this specification are to beunderstood as “extending or spreading from a centre outwards”, thecentre in this case being the longitudinal axis of the apparatus. Inthis specification. “radial” and “radially” do not limit the referenceddirection to one which is specifically at right angles to thelongitudinal axis.

The nozzle may be symmetrical about the centre line, whereby a lineextending perpendicular to the centre line between the nozzle surfacesat any point between the nozzle throat and nozzle outlet inclusive isbisected by the centre line.

The apparatus may further comprise first and second exterior surfaceswhich adjoin the first and second nozzle surfaces, respectively, at thenozzle outlet, and when viewed in cross section both the first andsecond exterior surfaces lie at an angle of substantially 90 degrees orless relative to the nozzle centre line. The first and second exteriorsurfaces may lie at the same angle relative to the nozzle centre line.Alternatively, the first and second exterior surfaces may lie at firstand second angles of 90 degrees or less relative to the nozzle centreline.

The nozzle may be asymmetrical about the centre line, whereby a lineconnecting the first and second nozzle surfaces at the nozzle outlet isdivided into two unequal portions by the centre line.

The apparatus may further comprise first and second exterior surfaceswhich adjoin the first and second nozzle surfaces, respectively, at thenozzle outlet, and when viewed in cross section at least the secondexterior surface lies at an angle of 90 degrees or less relative to thenozzle centre line.

The second nozzle surface may include a Coanda surface on a curved orconvex lip portion which projects radially outwards of the nozzleoutlet.

The nozzle may define a rotational angle of between 15 and 180 degreesabout the longitudinal axis. Alternatively, the nozzle may define arotational angle of 360 degrees about the longitudinal axis.

The nozzle outlet may be continuous around a portion of the perimeter ofthe apparatus covered by the rotational angle. Alternatively, the nozzleoutlet may be discontinuous around a portion of the perimeter of theapparatus covered by the rotational angle. The apparatus may furthercomprise one or more filler members which may be inserted into thenozzle outlet to create a discontinuity therein.

The first process fluid outlet may open into the nozzle from the firstnozzle surface in the nozzle throat or at a point downstream thereof.The process fluid outlet may be annular and extend circumferentiallyabout the longitudinal axis.

The apparatus may further comprise a second process fluid passage havingan inlet connectable to a supply of process fluid, and an outlet on thesecond nozzle surface, the outlet opening into the nozzle intermediatethe nozzle throat and the nozzle outlet.

According to a second aspect of the present invention, there is provideda mist generating apparatus having a longitudinal axis and comprising:

-   -   first and second opposing nozzle surfaces which define a nozzle        therebetween; and    -   a first process fluid passage having an inlet connectable to a        supply of process fluid, and a process fluid outlet on one of        the first and second nozzle surfaces such that the process fluid        outlet opens into the nozzle;    -   wherein the nozzle has a nozzle inlet connectable to a supply of        driving fluid, a nozzle outlet, and a throat portion        intermediate the nozzle inlet and nozzle outlet, wherein the        nozzle throat has a cross sectional area which is less than that        of either the nozzle inlet or the nozzle outlet;    -   wherein the nozzle extends radially away from the longitudinal        axis such that the nozzle defines a rotational angle about the        longitudinal axis; and    -   wherein the second nozzle surface includes a Coanda surface on a        lip portion which projects radially outwards of the nozzle        outlet.

The nozzle may define a rotational angle of between 15 and 180 degreesabout the longitudinal axis. Alternatively, the nozzle may define arotational angle of 360 degrees about the longitudinal axis.

The nozzle outlet may be continuous around a portion of the perimeter ofthe apparatus covered by the rotational angle. Alternatively, the nozzleoutlet may be discontinuous around a portion of the perimeter of theapparatus covered by the rotational angle. The apparatus may furthercomprise one or more filler members which may be inserted into thenozzle outlet to create a discontinuity therein.

The first process fluid outlet may open into the nozzle from the firstnozzle surface in the nozzle throat or at a point downstream thereof.The process fluid outlet may be annular and extend circumferentiallyabout the longitudinal axis.

The apparatus may further comprise a second process fluid passage havingan inlet connectable to a supply of process fluid, and an outlet on thesecond nozzle surface, the outlet opening into the nozzle intermediatethe nozzle throat and the nozzle outlet.

According to a third aspect of the invention, there is provided a methodof generating a mist with a mist generating apparatus having alongitudinal axis, the method comprising:

-   -   supplying a flow of driving fluid to a nozzle extending radially        away from the longitudinal axis such that the nozzle defines a        rotational angle about the longitudinal axis, the nozzle defined        between first and second opposing nozzle surfaces of the        apparatus and comprising a nozzle inlet, a nozzle outlet, and a        nozzle throat intermediate the nozzle inlet and nozzle outlet,        and the nozzle throat having a cross sectional area which is        less than that of both the nozzle inlet and nozzle outlet, and a        centre line extending from the nozzle throat to the nozzle        outlet at an angle of between 50 and 80 degrees relative to the        longitudinal axis;    -   supplying a process fluid from a process fluid outlet on one of        the first and second nozzle surfaces to the nozzle in the nozzle        throat or at a point downstream thereof;    -   accelerating the flow of driving fluid as it passes through the        nozzle throat, whereby the accelerated driving fluid atomises        the process fluid exiting the process fluid outlet to form a        mist comprising a dispersed phase of process fluid droplets in a        continuous vapour phase of driving fluid; and    -   spraying the mist from the nozzle radially of the longitudinal        axis at the angle of between 50 and 80 degrees relative to the        longitudinal axis.

The nozzle outlet may be continuous around a portion of the perimeter ofthe apparatus covered by the rotational angle. Alternatively, the nozzleoutlet may be discontinuous around a portion of the perimeter of theapparatus covered by the rotational angle. In the latter case, themethod may comprise an initial step of inserting one or more fillermembers into the nozzle outlet to form discontinuities therein.

According to a fourth aspect of the invention, there is provided amethod of generating a mist with a mist generating apparatus having alongitudinal axis, the method comprising:

-   -   supplying a flow of driving fluid to a nozzle extending radially        away from the longitudinal axis such that the nozzle defines a        rotational angle about the longitudinal axis, the nozzle defined        between first and second opposing nozzle surfaces of the        apparatus and comprising a nozzle inlet, a nozzle outlet, and a        nozzle throat intermediate the nozzle inlet and nozzle outlet,        and the nozzle throat having a cross sectional area which is        less than that of both the nozzle inlet and nozzle outlet, and        the second nozzle surface includes a downwardly-curving Coanda        surface on a lip portion which projects radially outwards of the        nozzle outlet;    -   supplying a process fluid from a process fluid outlet on one of        the first and second nozzle surfaces to the nozzle in the nozzle        throat or at a point downstream thereof;    -   accelerating the flow of driving fluid as it passes through the        nozzle throat, whereby the accelerated driving fluid atomises        the process fluid exiting the process fluid outlet to form a        mist comprising a dispersed phase of process fluid droplets in a        continuous vapour phase of driving fluid; and    -   spraying the mist from the nozzle radially of the longitudinal        axis towards the Coanda surface such that at least a portion of        the mist is directed downwards by the Coanda surface.

The nozzle outlet may be continuous around a portion of the perimeter ofthe apparatus covered by the rotational angle. Alternatively, the nozzleoutlet may be discontinuous around a portion of the perimeter of theapparatus covered by the rotational. In the latter case, the method maycomprise an initial step of inserting one or more filler members intothe nozzle outlet to form discontinuities therein.

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a cross section through a first embodiment of a mistgenerating apparatus;

FIG. 2 is a cross section through the spray head of the apparatus shownin FIG. 1;

FIGS. 3-6 are schematic cross sections through alternative embodimentsof the mist generating apparatus;

FIGS. 7-1.1 are schematic cross sections of alternative embodiments ofnozzle for use in the mist generating apparatus;

FIG. 12 is a schematic cross section of a further alternative embodimentof nozzle for use in a mist generating apparatus; and

FIG. 13 is a schematic cross section showing a mist generating apparatuslocated within a recess.

FIG. 1 shows a first embodiment of a mist generating apparatus,generally designated 10. In the illustrated embodiment the apparatus 10is housed within a recess 12 in the upper surface 14 of the volume intowhich the apparatus is to spray a mist. This volume may be in, forexample, a warehouse, operating theatre, mass transit system vehicle, orthe cargo hold of an aircraft. In these and other applications theapparatus 10 may be utilised as part of a fire suppression system, withthe apparatus 10 recessed so that personnel, equipment, stored goods andthe like do not come into contact with the apparatus 10. However, itshould be understood that the present invention is not limited torecessed applications alone, as will be discussed below.

The apparatus 10 comprises a substantially cylindrical body 20 having afirst end 22 located above the recess 12 for connection to fluid supplylines (not shown), and a second end 24 projecting into the recess 12.The apparatus 10 further comprises a spray head 30 which is attached tothe second end 24 of the body 20. Two fluid passages 26,28 are definedwithin the body 20. The first passage 26 is co-axial with a longitudinalaxis L of the apparatus 10 and supplies a driving fluid from a drivingfluid supply (not shown) to the spray head 30. The second passage 28 isradially offset from the longitudinal axis L but is substantiallyparallel thereto. The second passage 28 supplies a process fluid from aprocess fluid supply (not shown) to the spray head 30. The secondpassage 28 preferably comprises an upstream section 28 a and adownstream section 28 b. Both sections 28 a,28 b of the second passage28 are substantially parallel to the longitudinal axis L but thedownstream section 28 b is radially inward of the upstream section 28 asuch that an offset exists in the radial direction between the twosections 28 a,28 b of the second passage 28. The second passage 28 opensinto an annular channel at the second end 24 of the body 20. With thespray head 30 attached as shown in FIG. 1, the annular channel becomesan annular chamber 29.

The spray head 30 is shown in more detail in FIG. 2. The spray head 30comprises a generally cylindrical spray member 32 having a first end 34and a second end 36. The first end 34 includes a radially extendingflange 35 and is adapted to be attached to the second end 24 of the body20, as shown in FIG. 1. The spray member includes a blind bore 37 whichis co-axial with the longitudinal axis L shared by the apparatus 10 andspray head 30. As shown in FIG. 1, the bore 37 connects with the firstpassage 26 so as to receive driving fluid from the first passage 26.Extending radially outwards from the bore 37 are a number of nozzlesupply passages 38.

The flange 35 includes a plurality of passages 39 circumferentiallyspaced about the longitudinal axis L, which in use allow the annularchamber 29 in the body 20 to communicate with the spray head 30. Anannular spacer 40 has a first side 41 which abuts the flange 30 suchthat an annular space is defined between an inner surface 42 of thefirst spacer 40 and the spray member 32. The spray member 32 includes aradially-projecting lip 44, and an annular inner insert 46 is broughtinto abutment with the lip 44 and a second side 43 of the spacer 40,whereby an annular first process fluid chamber 48 is defined between thespray member 32, the first spacer 40 and the inner insert 46. The innerinsert 46 includes a longitudinal passage 47, which allows fluidcommunication between upstream and downstream sides of the inner insert46, and hence downstream from the first process fluid chamber 48.

An annular outer insert 50 as a first side 51 which abuts the secondside 43 of the spacer 40, and an internal surface having a first portion52 whose internal diameter is greater than that of a second portion 53.The difference in internal diameter between the first and secondportions 52,53 of the outer insert 50 forms a locking surface 54, whichin use engages the downstream side of the inner insert 46 in order tosecure the inner insert 46 in position against the spacer 40 and lip 44of the spray member 32. A second process fluid chamber 56 is definedbetween the second portion 53 of the outer insert 50 and an outersurface 49 of the insert 46, whereby the passage 47 in the inner insert46 opens into the second process fluid chamber 56.

The second end 36 of the spray member 32 includes an axial projection60. A cup member 70 has an open first end 72 and a closed second end 74.The cup member 70 defines an internal space whose internal diameter issubstantially the same as the external diameter of the second end 36 ofthe spray member 32. Consequently, the cup member 70 fits over thesecond end 36 of the spray member 32 such that the closed end 74 of thecup 70 abuts the axial projection 60. As a result, a third annularprocess fluid chamber 76 is defined between the cup member 70 and thesecond end 36 of the spray member 32. A plurality of axially extendingpassages 78 in the spray member 32 permit fluid communication betweenthe first and third process fluid chambers 48,76. The cup member 70 alsoincludes a number of circumferentially-spaced passages 80, which permitfluid flow from the interior to the exterior of the cup member 70, andhence outwardly from the third process fluid chamber 76.

Finally, an annular cap 90 is fitted over the exterior of the cup 70with at least a portion of the inner diameter of the cap 90 beinggreater than the outer diameter of the cup 70, such that a fourthprocess fluid chamber 92 is defined between the cap 90 and cup 70 at thelocation where the cup passages 80 open on the exterior of the cup 70.

It should be noted that a number of functional components have beenomitted from the drawings for illustrative purposes. Specifically, whereappropriate the various components would include circumferential groovesand O-ring seals located in those grooves so as to provide fluid sealsbetween each of the components and also to ensure that the apparatus asa whole is airtight. Additionally, a plurality of known mechanicalfixtures such as, for example, screws, nuts and bolts are not shown butwould be incorporated into the apparatus so as to secure the componentsin the positions shown in the figures.

As can be seen in FIG. 2, the cup 70 and cap 90 do not abut the innerand outer inserts 46,50. Instead, the engagement of the second end 74 ofthe cup 70 with the axial projection 60 on the spray member 32 ensuresthat a gap is present between the first end 72 of the cup 70 and theinner insert 46. Similarly, the inner surface of the cap 90 and outersurface of the cup 70 engage in such a way that the surface of the cap90 adjacent the outer insert 50 provides a gap between those twocomponents. It is the inner and outer inserts 46,50, the cup 70, cap 90and gaps therebetween which define the nozzle of the spray head 32. Thelower surfaces of the inner and outer inserts 46,50 collectively providea first nozzle surface 100, which opposes a second nozzle surface 102collectively provided by the upper surface of the cap 90 and the firstend 72 of the cup 70 on the other side of the gap. A nozzle inlet 104 isdefined between the inner insert 46 and first end 72 of the cup 70, andis in fluid communication with the nozzle supply passages 38. A nozzleoutlet 108 is defined between the outer insert 50 and cap 90. The nozzlealso includes a throat portion 106 intermediate the nozzle inlet 104 andnozzle outlet 108, the nozzle throat 106 having a cross sectional areawhich is less than that of both the nozzle inlet 104 and nozzle outlet108. In this preferred embodiment, the reduction in cross sectional areafrom the nozzle inlet 104 to the throat 106 is achieved by the narrowingof the gap in the radial direction between the inner insert 46 and firstend 72 of the cup 70. Whilst the gap then remains substantially constantfrom the nozzle throat 106 to the nozzle outlet 108, the cross sectionalarea at the outlet 108 is greater than at the throat due to the 360degree rotational angle of the nozzle about the longitudinal axis L ofthe apparatus and the fact that the outlet 108 is at a greater distancethan the nozzle throat 106 from the longitudinal axis L in a directionperpendicular to the longitudinal axis L.

A nozzle adjustment mechanism may also be incorporated in the apparatus.As best seen in FIG. 1, the adjustment mechanism may comprise a numberof threaded adjusters 130 which are received within threaded apertures132 extending through the cap 90 so that an inner end of each adjuster130 lies against the first nozzle surface 100 on the outer insert 50. Anouter end of each adjuster 130 lies proud of the cap 90 so that it maybe rotated clockwise or counter-clockwise. Rotation of the adjusters 130clockwise will push the cap 90 and cup 70 attached thereto away from theinner and outer inserts 46, 50, whilst counter-clockwise rotation willresult in the cap 90 and cup 70 moving closer to the inner and outerinserts 46,50. In this way, the nozzle adjustment mechanism can adjustthe distance between the first and second nozzle surfaces 100,102 andthus vary the velocity and/or flow rate of the driving fluid and theresultant degree of atomisation of the process fluid.

A small gap also exists between the inner and outer inserts 46,50, whichacts as a first process fluid outlet 110 allowing fluid communicationbetween the second process fluid chamber 56 and the nozzle. A similararrangement exists between the cup 70 and cap 90, wherein the gapbetween those two components acts as a second process fluid outlet 112allowing fluid communication between the fourth process fluid chamber 92and the nozzle. The nozzle has a centre line CL which when the nozzle isviewed in cross section extends through first and second points in thenozzle throat 106 and nozzle outlet 108, respectively, where those firstand second points are the midpoints between the first and secondsurfaces at the nozzle throat 106 and nozzle outlet 108, respectively.The centre line lies at an angle α of between 50 and 80 degrees relativeto the longitudinal axis L.

The outer insert 50 and cap 90 have respective first and second exteriorsurfaces 120,122 which adjoin the first and second nozzle surfaces100,102, respectively, at the nozzle outlet 108. When viewed in crosssection in the manner shown in both FIGS. 1 and 2, both the first andsecond exterior surfaces 120,122 lie at an angle β of substantially 90degrees or less relative to the nozzle centre line CL.

The manner in which the apparatus shown in FIGS. 1 and 2 operates willnow be described. Initially, a first pressurised supply of process fluid(not shown) is connected to the inlet of the second passage 28. Theprocess fluid in this example is water. The process fluid passes fromthe passage 28 into the annular chamber 29, and from there into thefirst process fluid chamber 48 via the passages 39. From there, theprocess fluid exits the first process fluid chamber 48 via the passage47 and enters the second process fluid chamber 56. The process fluidleaves the second process fluid chamber 56 via the first process fluidoutlet 110 defined between the inner and outer inserts 46,50. The firstoutlet 110 has a smaller cross sectional area than that of the secondchamber 56, with the result that the process fluid exits through theoutlet 110 as a thin ring of process fluid.

At the same time as the process fluid passes from the first to thesecond process fluid chambers 48,56 via the passage 47, a portion of theprocess fluid is also passing from the first process fluid chamber 48 tothe third process fluid chamber 76 via the passages 78. From there, theprocess fluid flows into the fourth process fluid chamber 92 via thepassages 80 provided in the cup 70. The process fluid leaves the fourthprocess fluid chamber 92 via the second process fluid outlet 112 definedbetween the cup 70 and cap 90. The second outlet 112 has a smaller crosssectional area than that of the fourth chamber 92, with the result thatthe process fluid exits through the outlet 112 as a thin ring of processfluid. Thus, both streams of process fluid enter the nozzle from theirrespective outlets 110,112 as thin annuli of process fluid.

As the process fluid enters the apparatus 10, so does a supply ofdriving fluid. The driving fluid, preferably nitrogen, enters the firstpassage 26 in the body 20. Consequently, driving fluid enters the blindbore 37 in the spray member 32, and from there it passes through each ofthe nozzle supply passages 38 into the nozzle inlet 104 defined betweenthe inner surfaces of the inner insert 46 and cup 70.

The preferred supply pressures of the driving and process fluids, aswell as the preferred mass flow ratios between the two fluid supplies,are dependent on the particular application for which the apparatus isto be used. For example, in a decontamination application the mass flowratio between the process fluid and driving fluid is preferably between1:1 and 2:1. In other words, in the preferred range the mass flow ratiowould be 1-2 kg of process fluid for every 1 kg of driving fluid. Inthis application the preferred supply pressure ranges are 2-4 bar(gauge) for the process fluid and 3.5-4.5 bar (gauge) for the drivingfluid. In a fire suppression application the mass flow ratio between thetwo fluids is between 3:1 and 8:1, with 3-8 kg of process fluid forevery 1 kg of driving fluid. The supply pressure ranges for a firesuppression application are preferably 440 bar (gauge) for the processfluid and 5-12 bar (gauge) for the driving fluid.

The total cross sectional area of the nozzle supply passages 38 isgreater than that of the nozzle throat 106 defined between the innerinsert 46 and cup 70. As the nozzle extends in the radial directiontowards the nozzle outlet 108, its cross sectional area increases again.As the driving fluid enters the nozzle the reduced cross sectional areaof the nozzle throat 106 causes the driving fluid to undergo asignificant acceleration. This acceleration causes the velocity of thedriving fluid to significantly increase, preferably to at least sonicvelocity and most preferably to a supersonic velocity depending on theparameters of the driving fluid supplied to the apparatus. The drivingfluid then comes into contact with the twin streams of process fluidexiting the first and second outlets 110,112.

As the driving and process fluids come into contact with one another anenergy transfer takes place, primarily as a result of mass and momentumtransfer between the high velocity driving fluid and the relatively lowvelocity process fluid. This energy transfer imparts a shearing force onthe process fluid streams, leading to the atomisation of the processfluid. This atomisation leads to the formation of a mist made up of adispersed phase of process fluid droplets in a continuous vapour phaseof driving fluid. The mist sprays from the apparatus 10 at the angle αrelative to the longitudinal axis L, and over a preferred rotationalspray angle about the axis L of substantially 360 degrees. With theexterior surfaces 120,122 lying at the angle β of substantially 90degrees or less relative to the centre line CL of the nozzle, the mistdroplets spraying from the nozzle outlet 108 are not subject to anyCoanda effects which would attract them to those exterior surfaces120,122.

FIGS. 3 to 6 show schematic cross sections of alternative embodiments ofthe mist generating apparatus. These alternative embodiments are similarto the first embodiment shown in FIGS. 1 and 2, in that they each employa nozzle whose centre line CL, when viewed in cross section, is at theangle α of between 50 and 80 degrees relative to the longitudinal axis Lof the apparatus, and each has first and second exterior surfaces120,122 which—when also viewed in cross section as per these FIGS. 3 to6—lie at the angle β of substantially 90 degrees or less relative to thecentre line CL. Where these embodiments differ from each other and thefirst embodiment is in their overall shape. The second embodiment shownin FIG. 3 combines a generally cylindrical body 22Q with a conical sprayhead 230. FIG. 4 illustrates a third embodiment in which the entireapparatus is conical, rather than just the spray head. FIG. 5illustrates a fourth embodiment similar to the first embodiment, inwhich the body 420 is generally cylindrical and the spray head 430 isfrustoconical. However, in the fourth embodiment an end 434 of the sprayhead 430 remote from the body 420 is concave. FIG. 6 illustrates a fifthembodiment in which the spray head 530 has a larger diameter than thatof the generally cylindrical body 520, as well as having an end 534remote from the body 520 which is concave. As the spray head 530 has aconcave end 534 and a larger diameter than the body 520, the angles β atwhich the first and second exterior surfaces 120,122 lie relative to thenozzle centre line CL are much shallower in the fifth embodiment,creating a pair of “knife edges” at the nozzle outlet 508.

FIGS. 7 to 11 show schematic cross sections of various embodiments ofnozzle which may form part of the present invention. Only one half ofeach nozzle cross section is shown for illustrative purposes, with itbeing understood that the other half of the nozzle would be a mirrorimage of the half shown, about the longitudinal axis L. Each nozzleemployed in the present invention is a convergent-divergent nozzle. Thisterm is to be understood as referring to a nozzle whose cross sectionalarea reduces from nozzle inlet to a nozzle throat, and then increasesagain from the nozzle throat to nozzle outlet. These changes in crosssectional area are linear, or at least gradual, such that the surfacesdefining the nozzle are smooth and free from any steps or protrusionscaused by sudden increases or decreases in cross sectional area withinthe nozzle. As with the nozzle described above, each of these nozzleshas a centre line CL which in cross section lies at an angle α ofbetween 50 and 80 degrees relative to the longitudinal axis L.Furthermore, these nozzles themselves generate a mist in the same manneras described above with respect to the first embodiment of the mistgenerating apparatus.

FIG. 7 shows a first embodiment of spray head 630 having a nozzledefined by first and second opposing nozzle surfaces 600,602. The nozzlehas a nozzle inlet 604 connected to a driving fluid supply (not shown),a nozzle outlet 608, and a nozzle throat 606 intermediate the nozzleinlet 604 and nozzle outlet 608. The throat 606 has a cross sectionalarea which is less than that of the inlet 604 and outlet 608. In thisembodiment, the nozzle surfaces 600,602 downstream of the nozzle throatlie at an angle φ relative to the nozzle centre line CL when viewed incross section. In the same view the exterior surfaces 620,622 of thespray head 630 lie at an angle β of substantially 90 degrees relative tothe nozzle centre line CL. The nozzle includes at least one processfluid outlet 610 on the first nozzle surface 600. Preferably, there isalso a process fluid outlet 612 on the second nozzle surface 602. Theoutlets 610,612 open into the nozzle in the nozzle throat 606 ordownstream thereof.

FIG. 8 shows a second embodiment of spray head 730, which employs anozzle identical to that used in the first embodiment of the apparatusand shown in detail in FIG. 2. This second embodiment is included hereso as to more clearly show the relationships between the varioussurfaces of the nozzle and spray head. The nozzle is defined by firstand second opposing nozzle surfaces 700,702. The nozzle has a nozzleinlet 704 connected to a driving fluid supply (not shown), a nozzleoutlet 708, and a nozzle throat 706 intermediate the nozzle inlet 704and nozzle outlet 708. The throat 706 has a cross sectional area whichis less than that of the inlet 704 and outlet 708. In this embodiment,the nozzle surfaces 700,702 downstream of the nozzle throat 706 liesubstantially parallel to the nozzle centre line CL. Although the nozzlesurfaces 700,702 do not diverge from one another downstream of thenozzle throat 706, the nozzle is still a convergent divergent nozzlewhose cross sectional area at the outlet 708 is greater than that of thethroat 706. This is because the nozzle covers a 360 degree rotationalangle about the longitudinal axis L and the nozzle outlet 708 is at agreater distance than the nozzle throat 106 from the longitudinal axis Lin a direction perpendicular to the longitudinal axis L, so the nozzleoutlet 708 has a greater circumference than the nozzle throat 706, andhence a larger cross sectional area despite the nozzle surfaces 700,702maintaining a constant gap from the nozzle throat 706 to the nozzleoutlet 708.

When viewed in cross section as in FIG. 8, the exterior surfaces 720,722of the spray head 732 lie at an angle β of substantially 90 degreesrelative to the nozzle centre line CL. The nozzle includes at least oneprocess fluid outlet 710 on the first nozzle surface 700. Preferably,there is also a process fluid outlet 712 on the second nozzle surface702. The outlets 710,712 open into the nozzle in the nozzle throat 706or downstream thereof.

Each of the preceding embodiments utilises a nozzle which is symmetricalabout the nozzle centre line. A symmetrical nozzle is one in which aline extending perpendicular to the centre line across the nozzlebetween the opposing nozzle surfaces at any point between the nozzlethroat and nozzle outlet inclusive is bisected by the centre line.Referring specifically to FIGS. 7 and 8, lines T and O can be seenextending perpendicular to the centre line CL across the nozzle at thenozzle throat 606,706 and nozzle outlet 608,708, respectively. Each lineT,O is divided into two equal length parts T1,T2,O1,O2 by the centreline CL.

FIG. 9 shows a third embodiment of spray head 830 having a nozzledefined by first and second opposing nozzle surfaces 800,802. The thirdembodiment of nozzle is similar to the first embodiment shown in FIG. 7,but in the third embodiment a line X connecting the first and secondnozzle surfaces 800, 802 across the nozzle outlet 808 is divided intotwo unequal length portions X1,X2 by the centre line CL. This means thatthe third embodiment of nozzle is asymmetrical about the nozzle centreline CL, rather than symmetrical in the manner of the previousembodiments. When viewed in cross section as in FIG. 8, the secondexterior surface 822 of the spray head 832 lies at an angle β of lessthan 90 degrees relative to the nozzle centre line CL. The increasedlength of the first nozzle surface 800 creates a radial lip 821, whichin conjunction with the second exterior surface 822 ensures that theensuing mist sprays outwards and downwards.

FIG. 10 shows a fourth embodiment of spray head 930 having a nozzledefined by first and second opposing nozzle surfaces 900,902. The fourthembodiment of nozzle is similar to the third embodiment of FIG. 9, inthat a line X connecting the first and second nozzle surfaces 900, 902across the nozzle outlet 908 is divided into two unequal length portionsX1,X2 by the centre line CL. This means that like the third embodimentthe fourth embodiment of nozzle is also asymmetrical about the nozzlecentre line CL. The increased length of the first nozzle surface 900also creates a radial lip 921, which has a first exterior surface 920.Both the first exterior surface 920, and the second exterior surface 922which adjoins the second nozzle surface 902, lie at respective anglesβ1,β2 of less than 90 degrees relative to the nozzle centre line CL,when viewed in cross section as here in FIG. 10.

FIG. 11 shows a fifth embodiment of spray head 1030 having a nozzlewhich is defined by first and second opposing nozzle surfaces 1000,1002.The nozzle is similar to the second embodiment shown in FIG. 8, in thatthe nozzle surfaces 1000,1002 downstream of the nozzle throat 1006 liesubstantially parallel to the nozzle centre line CL when viewed in crosssection. Where this embodiment differs from the second embodiment isthat the second nozzle surface 1002 includes a lip portion 1003 whichprojects radially outwards from the nozzle outlet 1008. The lip portion1003 has a curved Coanda surface 1004 which creates a Coanda effect onthe mist issuing from the outlet 1008, encouraging the mist to followthe surface of the lip 1003 in an outward and downward direction. Inthis embodiment, the first and second process fluid outlets 1010,1012enter the nozzle downstream of the nozzle throat 1006.

The apparatus and nozzle of the present invention can spray a mist ofdroplets over a rotational angle of up to 360 degrees about thelongitudinal axis of the apparatus. Furthermore, by providing a nozzlewhose centre line is at between 50 and 80 degrees relative to thelongitudinal axis when viewed in cross section, the apparatus maycontinue to quickly fill a volume with mist but prevents theconcentration and coalescence of droplets on the surface to which theapparatus is mounted. Similarly, if the apparatus must be mounted in arecess for operational reasons, the angling of the nozzle and its centreline ensures that the mist is not concentrated in the recess and insteadenters the volume to be filled. The performance of the apparatus can befurther enhanced by ensuring that at least one, if not both, of theexterior apparatus surfaces adjoining the nozzle outlet lies at angle of90 degrees or less relative to the nozzle centre line when the nozzle isviewed in cross section. This removes the possibility of the mistdroplets being attracted to the exterior surfaces of the apparatusinstead of travelling out into the volume. An alternative enhancement isto provide the projecting lower lip having the curved Coanda surface soas to attract the droplets to the lip but then direct them downwardsinto the volume by way of the Coanda effect created by the surface.

FIG. 12 shows a schematic cross section of an alternative embodiment ofnozzle, which provides an alternative way in which to ensure that themist generated by the apparatus is issued in a generally downwarddirection. As with the embodiments of FIGS. 7 to 11, only one half ofthe nozzle is shown for illustrative purposes, with it being understoodthat the other half of the nozzle would be a mirror image of the halfshown, about the longitudinal axis L. Furthermore, this nozzle is also aconvergent-divergent nozzle of the type described above, and generates amist in the same manner as described above with respect to the firstembodiment of the mist generating apparatus.

Where the alternative nozzle of FIG. 12 differs from the previouslydescribed embodiments of nozzle is that the nozzle centre line CL is atan angle α of substantially 90 degrees relative to the longitudinal axisL when viewed in cross section as in FIG. 12. Thus, when the mistgenerating apparatus is mounted in a substantially vertical orientationthe mist spraying from the nozzle will issue in a substantiallyhorizontal direction. The nozzle is defined by first and second opposingnozzle surfaces 1100,1102. The nozzle surfaces 1100,1102 downstream ofthe nozzle throat 1106 lie substantially parallel to the nozzle centreline CL. The second nozzle surface 1102 includes a lip portion 1103which projects radially outwards from the nozzle outlet 1108. The lipportion 1103 has a curved Coanda surface 1104 which creates a Coandaeffect on the mist issuing from the outlet 1108, encouraging the mist tofollow the surface of the lip 1103 in a downward direction. The lipportion 1103 may be modified such that the upper surface 1104 ends in acutaway section having a sharp edge rather than the arrangement of FIG.12, where the upper surface 1104 ends with an exterior surface 1122which is generally at right angles to the centre line CL of the nozzle.

FIG. 13 illustrates schematically how any of the embodiments of mistgenerating apparatus described herein may be positioned within a recess.The illustrated apparatus 1210 shares many of the components alreadydescribed above in respect of the other embodiments, and thosecomponents will not be described again in detail here. The apparatus1210 is located within a recess 1212 having a recessed surface 1213. Theapparatus 1210 is positioned such that the cylindrical body 1220 ispartially located in the recessed surface 1213 and extends out into therecess 1212 from the surface 1213. The apparatus 1210 has a longitudinalaxis L and the nozzle outlet 1208 of the apparatus is located a firstaxial distance d1 from the recessed surface 1213. The free, or exposed,end 1234 of the apparatus 1210 is a second axial distance d2 from thenozzle outlet 1208. The recess 1212 has an overall depth D, which is thedistance from the recessed surface 1213 to the plane of the ceiling, orupper surface, 1214 of the volume into which the apparatus is to spray amist. To ensure the proper positioning of the apparatus, the formulaD≧d1+d2 must be adhered to. In this way, the apparatus is “fullyrecessed”, by which it is meant that the exposed end and nozzle of theapparatus are as close to the plane of the upper surface 1214 aspossible whilst remaining within the recess and protected.

The recess 1212 may be circular with tapered sides, as shown in FIG. 13.Alternatively, the recess may be square- or rectangular-shaped, with orwithout tapered sides. Any corners within the recess may have a chamferor radius of curvature to ensure that each corner has a smooth surfacewith no sharp angles.

The driving fluid utilised in the present invention is preferablycompressed air or nitrogen. Alternatively, the driving fluid may becarbon dioxide or steam. The process fluid is preferably water, but mayalternatively be liquid fire suppressant decontaminant, for example.

Although a preferred application for the present invention is as part ofa fire suppression system, the present invention is not limited to thisparticular application. The present invention may also be employed in adecontamination or cooling system, for example.

Whilst the preferred embodiments of the present invention comprise firstand second process fluid outlets into the nozzle, the invention is notlimited to this arrangement. The invention may instead comprise only asingle process fluid outlet on either the first or second nozzlesurface.

Whilst the preferred embodiments of the nozzle define a rotational angleof substantially 360 degrees, the nozzle may define a smaller rotationalangle as required, for example if the apparatus is deployed in thecorner of a volume or room. The nozzle may instead therefore define arotational angle of between 1 and 360 degrees or, most preferably inthis particular deployment, between 15 and 180 degrees about thelongitudinal axis. This facilitates the fitment of a nozzle within aconfined space such as the corner of a room. In the case of such a“limited angle” nozzle, the rotational angle of the process fluidoutlet(s) on one or both nozzle surfaces may be smaller than the overallrotational angle of the nozzle to reduce the possibility of the processfluids coming into contact with the internal nozzle walls which definethe outer boundaries of the reduced angle nozzle. This reduces the riskof large process fluid droplets being formed on these walls due tocoalescence.

In the preferred embodiments, the nozzle outlet is continuous around theportion of the circumference of the apparatus covered by the rotationalangle. However, the nozzle outlet may alternatively be discontinuousaround the portion of the circumference of the apparatus covered by therotational angle. In the latter case, the apparatus may further compriseone or more filler members which may be inserted into the nozzle outletto create discontinuities in the nozzle outlet. Alternatively, thenozzle could be formed with dividing members or similar integrallyformed therein to create the discontinuities in the nozzle outlet.However these discontinuities are created, they result in the nozzleoutlet being divided into a number of segments, with each segmentcovering a particular rotational angle about the longitudinal axis. Inthis case, the process fluid outlet(s) may also be discontinuous andcomprise a number of segments which cover the same rotational angles asthe nozzle outlet segments. Alternatively, each process fluid segmentmay cover a smaller rotational angle than its respective nozzle outletsegment to reduce the possibility of the process fluids coming intocontact with the internal nozzle walls which define the outer boundariesof the nozzle outlet segments. This reduces the risk of large processfluid droplets being formed on these walls due to coalescence.

Although the preferred range of angle α between the nozzle centre lineand the longitudinal axis of the apparatus is between 50 and 80 degrees,it may be desirable to limit the range of angle α to between 60 and 70degrees in order to limit the possibility of the droplets issuing fromthe nozzle being attracted to one another or the surface upon which thedevice is mounted.

Although preferred that the apparatus is mounted on a substantiallyhorizontal surface, the present invention is not limited to thisparticular arrangement. Instead, the apparatus could alternatively bemounted on a wall or other substantially vertical surface, or else theapparatus could be mounted in a recess on such a surface.

These and other modifications and improvements may be incorporatedwithout departing from the scope of the present invention.

What is claimed is:
 1. A mist generating apparatus having a longitudinalaxis and comprising: first and second opposing nozzle surfaces whichdefine a nozzle therebetween; and a first process fluid passage havingan inlet connectable to a supply of process fluid, and a process fluidoutlet on one of the first and second nozzle surfaces such that theprocess fluid outlet opens into the nozzle; wherein the nozzle has anozzle inlet connectable to a supply of driving fluid, a nozzle outlet,and a throat portion intermediate the nozzle inlet and nozzle outlet,wherein the nozzle throat has a cross sectional area which is less thanthat of both the nozzle inlet and the nozzle outlet; wherein the nozzleextends radially away from the longitudinal axis such that the nozzledefines a rotational angle about the longitudinal axis; and wherein acentre line of the nozzle extending from the nozzle throat to the nozzleoutlet is at an angle of between 50 and 80 degrees relative to thelongitudinal axis.
 2. The apparatus of claim 1, further comprising firstand second exterior surfaces which adjoin the first and second nozzlesurfaces, respectively, at the nozzle outlet, and when viewed in crosssection both the first and second exterior surfaces lie at an angle ofsubstantially 90 degrees or less relative to the nozzle centre line. 3.The apparatus of claim 2, wherein the first and second exterior surfaceslie at the same angle relative to the nozzle centre line.
 4. Theapparatus of claim 2, wherein the first and second exterior surfaces lieat first and second angles of 90 degrees or less relative to the nozzlecentre line.
 5. The apparatus of claim 1, wherein the nozzle isasymmetrical about the centre line, whereby a line connecting the firstand second nozzle surfaces at the nozzle outlet is divided into twounequal portions by the centre line.
 6. The apparatus of claim 5,further comprising first and second exterior surfaces which adjoin thefirst and second nozzle surfaces, respectively, at the nozzle outlet,and when viewed in cross section at least the second exterior surfacelies at an angle of 90 degrees or less relative to the nozzle centreline.
 7. The apparatus of claim 1, wherein the second nozzle surfaceincludes a Coanda surface on a curved or convex lip portion whichprojects radially outward of the nozzle outlet.
 8. The apparatus ofclaim 1, wherein the nozzle defines a rotational angle of between 15 and180 degrees about the longitudinal axis.
 9. The apparatus of claim 1,wherein the nozzle outlet is continuous around a portion of theperimeter of the apparatus covered by the rotational angle.
 10. Theapparatus of claim 1, wherein the nozzle outlet is discontinuous arounda portion of the perimeter of the apparatus covered by the rotationalangle.
 11. The apparatus of claim 10, further comprising one or morefiller members which are inserted into the nozzle outlet to create adiscontinuity therein.
 12. The apparatus of claim 1, wherein the processfluid outlet opens into the nozzle from the first nozzle surface in thenozzle throat or at a point downstream thereof.
 13. The apparatus ofclaim 1, wherein the process fluid outlet is annular and extendscircumferentially about the longitudinal axis.
 14. The apparatus ofclaim 1, further comprising a second process fluid passage having aninlet connectable to a supply of process fluid, and an outlet on thesecond nozzle surface, the outlet opening into the nozzle intermediatethe nozzle throat and the nozzle outlet.
 15. A mist generating apparatushaving a longitudinal axis and comprising: first and second opposingnozzle surfaces which define a nozzle therebetween; and a first processfluid passage having an inlet connectable to a supply of process fluid,and a process fluid outlet on one of the first and second nozzlesurfaces such that the process fluid outlet opens into the nozzle;wherein the nozzle has a nozzle inlet connectable to a supply of drivingfluid, a nozzle outlet, and a throat portion intermediate the nozzleinlet and nozzle outlet, wherein the nozzle throat has a cross sectionalarea which is less than that of either the nozzle inlet or the nozzleoutlet; wherein the nozzle extends radially away from the longitudinalaxis such that the nozzle defines a rotational angle about thelongitudinal axis; and wherein the second nozzle surface includes aCoanda surface on a lip portion which projects radially outwards of thenozzle outlet.
 16. The apparatus of claim 15, wherein the nozzle definesa rotational angle of between 15 and 180 degrees about the longitudinalaxis.
 17. The apparatus of claim 15, wherein the nozzle outlet iscontinuous around a portion of the perimeter of the apparatus covered bythe rotational angle.
 18. The apparatus of claim 15, wherein the nozzleoutlet is discontinuous around a portion of the perimeter of theapparatus covered by the rotational angle.
 19. The apparatus of claim18, further comprising one or more filler members which are insertedinto the nozzle outlet to create a discontinuity therein.
 20. Theapparatus of claim 15, wherein the process fluid outlet opens into thenozzle from the first nozzle surface in the nozzle throat or at a pointdownstream thereof.
 21. The apparatus of claim 15, wherein the processfluid outlet is annular and extends circumferentially about thelongitudinal axis.
 22. The apparatus of claim 15, further comprising asecond process fluid passage having an inlet connectable to a supply ofprocess fluid, and an outlet on the second nozzle surface, the outletopening into the nozzle intermediate the nozzle throat and the nozzleoutlet.
 23. A method of generating a mist with a mist generatingapparatus having a longitudinal axis, the method comprising: supplying aflow of driving fluid to a nozzle extending radially away from thelongitudinal axis such that the nozzle defines a rotational angle aboutthe longitudinal axis, the nozzle defined between first and secondopposing nozzle surfaces of the apparatus and comprising a nozzle inlet,a nozzle outlet, and a nozzle throat intermediate the nozzle inlet andnozzle outlet, and the nozzle throat having a cross sectional area whichis less than that of both the nozzle inlet and nozzle outlet, and acentre line extending from the nozzle throat to the nozzle outlet at anangle of between 50 and 80 degrees relative to the longitudinal axis;supplying a process fluid from a process fluid outlet on one of thefirst and second nozzle surfaces to the nozzle in the nozzle throat orat a point downstream thereof; accelerating the flow of driving fluid asit passes through the nozzle throat, whereby the accelerated drivingfluid atomises the process fluid exiting the process fluid outlet toform a mist comprising a dispersed phase of process fluid droplets in acontinuous vapour phase of driving fluid; and spraying the mist from thenozzle radially of the longitudinal axis at the angle of between 50 and80 degrees relative to the longitudinal axis.
 24. The method of claim23, wherein the nozzle outlet is continuous around a portion of theperimeter of the apparatus covered by the rotational angle, and themethod comprises an initial step of inserting one or more filler membersinto the nozzle outlet to form discontinuities therein.
 25. A method ofgenerating a mist with a mist generating apparatus having a longitudinalaxis, the method comprising: supplying a flow of driving fluid to anozzle extending radially away from the longitudinal axis such that thenozzle defines a rotational angle about the longitudinal axis, thenozzle defined between first and second opposing nozzle surfaces of theapparatus and comprising a nozzle inlet, a nozzle outlet, and a nozzlethroat intermediate the nozzle inlet and nozzle outlet, and the nozzlethroat having a cross sectional area which is less than that of both thenozzle inlet and nozzle outlet, and the second nozzle surface includes adownwardly-curving Coanda surface on a lip portion which projectsradially outwards of the nozzle outlet; supplying a process fluid from aprocess fluid outlet on one of the first and second nozzle surfaces tothe nozzle in the nozzle throat or at a point downstream thereof;accelerating the flow of driving fluid as it passes through the nozzlethroat, whereby the accelerated driving fluid atomises the process fluidexiting the process fluid outlet to form a mist comprising a dispersedphase of process fluid droplets in a continuous vapour phase of drivingfluid; and spraying the mist from the nozzle radially of thelongitudinal axis towards the Coanda surface such that at least aportion of the mist is directed downwards by the Coanda surface.
 26. Themethod of claim 25, wherein the nozzle outlet is continuous around aportion of the perimeter of the apparatus covered by the rotationalangle, and the method comprises an initial step of inserting one or morefiller members into the nozzle outlet to form discontinuities therein.